Add structured version info for pyexpat

Feature or enhancement

pyexpat.EXPAT_VERSION (from XML_ExpatVersion()) and pyexpat.version_info (from XML_ExpatVersionInfo()) describe the Expat library loaded at runtime: both functions are compiled into libexpat from its XML_MAJOR_VERSION, XML_MINOR_VERSION and XML_MICRO_VERSION macros. The same macros evaluated in pyexpat.c give the version of the headers the module was built against, which is what the #if XML_COMBINED_VERSION >= ... checks in the module depend on. The two can differ when a system libexpat is used. The build-time version is not exposed to Python; it can only be inferred from which parser methods exist.

Add pyexpat.VERSION_INFO for the build-time version, and make pyexpat.version_info a named tuple.

Linked PRs

• gh-157474

从 pyexpat.c 开始，这里公开了 Expat 版本宏和运行时版本 API。跟踪现有的 VERSION_INFO 和 version_info 定义，然后验证构建时版本是否被单独公开，以及 version_info 是否具有命名元组行为。如果有 pyexpat API 测试，请检查这些测试，并确认当两个版本不同时，它们都能被正确报告。